Rotor blade



Aug. 12, 5 l. SlKO RSKY 2,606,728

' ROTOR BLADE Fiied Dec. 4, 1945 2 SHEETS-SHEET l IGOR 1.SIKORSKY v .INVENTOR ATTORNEY Aug. 12, 1952 I. I. YSIKOR'SKY 2,606,728

go r'bR BLADE Filed Dgc. 4, 1945 I 2 smmssm'r 2 IGOR l. SIKORISKY IYNVENTOR Patented Aug. 12, 1952 ROTOR BLADE Igor I. Sikorsky, Bridgeport, Conn., assignor to UnitedAircraft Corporation, East Hartford, Conn., a corporation of Delaware Application December 4, 1945, Serial No. 632,620

This invention relates to blades and more particularly to improvements in metal rotor blades for rotary wing aircraft, and is a continuationin-part of Patent No. 2,469,480, dated May. 10, 1949, issued to the present inventor.

An object of the invention is to provide a' simple, strong rotor blade.

Another object is the provision of a rotor blade having electrical heating means for preventing ing means for a rotor blade as set forth in any of thepreceding objects. y

A still further object is to provide improved trailing section construction ofpinterchangeable closed boxes forming segments of thetrailing edge of a rotor blade.

. Other objects and advantages will be, a parent from the specification and claims, and from the accompanying drawings which illustrate modifications of the invention.

In the drawings:

Fig.1 is a schematic side elevational view ofa helicopter, having improved blades and means for supplying hot gas thereto.

,Fig. 2 is an enlarged view of one of the rotor blades;

' Fig. 3 is a section on lines 3 --3 of Fig. 2;

Fig, 4 is, an enlarged perspective view showing a cross section of the structural member and the details of the blade trailing edge;

Fig. 5 is an enlarged perspective view showing the methodof attaching the blade support; i Fig. 6 is a detail ofpthe trailing edge fastening;

Fig. '7 is a view similar to Fig. 2 but of a modification of this invention; I

Fig. 8 is a perspective view of a portion of the presently preferred leading edge spar. assembled with a box unit of the trailing edge; V i

Fig. 9 is a detail sectional view taken along the lines 9-9 of Fig. 8; v q

Fig. 10 is a partial view of the root of the rotor blade showing the means for mounting, the blade portion tea connection bracket; .1 n Fig. 11 is a sectional view taken along the lines H-H qfFig.l;' 1 n Fig. 12 ,is a plan .view of the tip of therotor blade as it appears when removed from the blade; Fig. 131s a sectional view taken'along the lin'es 9 Claims. (Cl. 244-134) Fig.114 is a side elevational view'of another mount for the blade, and

Fig. id is a sectional View taken on the lines l5-l 5 of Fig. 14. Referring to Fig. 1, a helicopter fuselage I 0 carries an engine [2 driving a rotor shaft l4 on which are mounted rotor blades I6. An auxiliary propeller I8 is carried at one end'of the fuselage l0 and may be driven by rotor shaft l 4.

Each rotor blade I6 is built up of several members, including a structural member 20 forming the strength member of the blade, and also forming the leading edge thereof. The structural member 20 is preferably of uniform cross section from one end to the other. and has one or more partitions 22, 24 therein dividing the member into one or more tube-like sections 26, 28 extending the length thereof. This structural member may 'be I conveniently formed by an extrusion process, although it is not limited to such method o y. I

A tip-forming member 30 is secured, by welding or otherwise to'one end'of the structural member ,20, closing that end and forminga faired blade tip, which tip 30 is provided with one or more partitions 32 dividing the same into channels connecting with channels 26, 28 of the structural rnember 20. Apertures 34 in the blade tip provide outlets for theehambers. A support 36 preferably having a hinge connection 38 at one end thereof, supports the structural member 20 on 'therotor shaft M. The support 36 may include ,a plug 40 located inside of the structural member 20 and riveted (or otherwise secured) in place. A 'pl'atej42 covers the inner end of structural member 20 and closes off any openings not otherwise closed. a

The structure thus far described provides structural member 20 supported at one end by support 36 and having a tip-forming portion 30 onthe other end in which channels 26, 28 extend the full length of the blade between the support and the tip, and are provided with exits 34 at the tip.v A flexible conduit 44 may be utilized to conduct hot gases from the collector 46 to the interior of the structural member 20 for supplying hot gases thereto. If'the structural member 20 is made ofstainless steel, the hot gases may be the engine exhaust gases, but if the structural member is of aluminum, magnesium, or similar corrosive metals, in order to avoid corrosion, the hot gases maybe produced by runnin the engine exhaust .pipe 48 through a heat exchanger 50 and heating. air. The exhaust gas or the heated air may bepassed through a blower 52 and the flexible conduit 54 to the collector 46 and thence to size and area from the shank toward the tip of the blade, so as to give greater heat absorption at the blade tip where the gases will be cooler and the radiation greater (because of greater air speed of the blade tip) than at the blade shank.

The collector 46 is supported on shaft I4 and rotating plate 45 of the pitch changing mechanism. A sliding joint is provided between-the collector and the flexible conduit 54. The stationary portion of the sliding joint is supported on stationary plate 41 r of the pitch changing mechanism.

Small apertures 5'! may be provided in' the various partitions 22, 24 and 60 to permit bleeding of hot gasesfrom one passage to another and to the'interior of the trailing edge to be. presently described, to give a more uniform gradation of heat and pressure over the width of the blade.

The blade sectionis completed by fastening. V-shaped trailing. edge forming members or boxes 58 to the rear portion of structural member 20. The trailing edge. members are built up of sheet material forming the top portion 60, and the bottomportion 62. These sheets meet at one edge to form the blade trailing edge and are separated at the oppositefedgeto' ,thereby form the V'- shaped member.

Ribs 64 are fastened to the sheets as'by welding or riveting to reinforce and stiffenthe sheets. or partition 06 secured to or forming a partof structural member and the sheets 60 and 62 forming the top and bottom surfaces of the trailing edge member, overlap onto the structural member and are secured thereto by means such as rivets, screws,f or spring catches 60).

v A detail of one fastening means is shown in Fig. 6 in which the structural member 20 and sheet'GD are provided ivith registering holes and a tapered pin 'II is positioned therein by its sup,- porting spring I3.- v I Sheets 60 and 62. abut. adjacent sheets of the trailing edge portions on either side where. they overlap .thestructural member but are spaced from the adjacent sheets at the trailing edge as indicated at 10. An insert of strip material I2 secured to sheets 60 and E2 of one trailing edge portion underlies the joint formed with the adjac'ent trailing edge portion to close the gap I0. This. construction perinitsflexing of the structural member 20 in a fore-and-aft direction without distortion of the trailing edge. Such a construction also permits ready removal and replacement of any damagedtrailingedge portion and where the blade is made of uniform width throughout, provides ffor interchangeability whereby one trailing edge'm'ember may be used to replace a damaged section anywhere in the length of the blade.

, It has been foundthat under some conditions lift forceshave a tendencyto 'fiex the rotor blades in atransversedirection a greateramount than is desirable. By making the blade of uniform cross section throughout the length the" additional weightin 'the.outerportion of theblade tends,' under the action of l centrifugal force, to

The ribs 64 abut the plate provide a blade straightening force which reduces the flexing of the blade. A blade having a uniform section therefor, in addition to providing an easily fabricated structure, also produces a blade having superior structural qualities and improved performance.

- In that form of my invention shown in Fig. '7, ablade I00 ismade up of a strengthmember I02 also for forming the leading edge and is connected with a mounting member I04 for securing the blade I00 to the rotor head of the helicopter, or the like, trailing edge boxes I06, and a tip member I08, all of which members are secured together by suitable means to be described below to form a rugged but light weight rotor blade.

As best shown in Fig. 8, the strength member I02 has astreamlined curved exterior surface and has substantially vertical longitudinal strengthening webs IIO formed integral with the material forming the major surfaces of member I02, and which form a boritype spar or tubes running the entire length of the strength member I02 from the root to the tip of the blade. The tubes may conduct hot gases for de-icing purposes. The leading edge is substantially thickened and is also integral with those portions formingthe upper and lower surfaces of. member I02 and the strengthening webs IIO. As the strength member I02 is constructed, the portion IIZ, the webs H0 and also those sections forming the upper surfaces of'member I 02 are all of relatively thick section'to add strength and high fatigue resistance tot-he member. The thickened portion I I2 at the leading edge also balances the entire blade around a centerline II3 through the tubular section formed by the webs I I0, which centerline is located at approximately twenty-five'per cent of the chord of the entire blade. This centerline also occurs'on the feathering axis, the center of elasticity'and contains the center of percussion of the blade as finally assembled. Thus, the leading edge portion I I2 provides for greater strength at the leading edge so that the blade will be safe from damage in the event of striking small objects when hovering near the ground, or when in flight. The strength member I02 as constructed with the webs I0 and the arched'forward section including the thickened portion H2 is highly resistive to twisting moments acting upon the blade I00 to further enhance the value of the blade so constructed. Also, the transverse moments acting upon the strength member'l02 because of flapping of the bladedifferentially in advancing and retreating air, and the vibrations and harmonics of vibrations attendant to operation of the blade in an elastic medium, is such asto greatly reduce the stresses because the webs H0 and the leading edge II2 are integral and assume loads in the manner. of a composite beam but with no joints or connections which provide points for relative motion and hence weakness in such a beam.

The strength member I02 has rearwardly extended flanges I20 provided with lips I22 forming a longitudinal shoulder for receiving builtup flanges I24 of the box-like trailing edge forming members I06. The flanges I24 are made up of extensions of the skin I26 forming the cover for the box I08 and a longitudinal press plate I28 of channel shape which has forwardly extending ears fitting into the lips I22 lying beneath the skin, I20 and secured to the, lips with the skin by rivets I30, or the like. The plates I28 are riveted to ribs I32, which ribs are also riveted tothe skin I26. To this end ribs I32 have inturned flanges 132a overlying plates I28, which flanges are secured to plates I28 by rivets I32b, and upper and lower inturned flanges I320 which are secured to skin I26 by rivets I32'd. Ribs I32 are provided with strengthening dimples I34. The upper and j .lower skins I26 are fastened together to form a trailing edge I38. This trailing edge forms a bendable tab of similar action to the one disclosed in U. S. Patent No. 2,473,134, issued June 14, 1949, of H. W. Bonnett, which tab may be formed by bending as required to balance aerodynamic forces acting on the blade. The adjacent boxes I06 may be in contact with each other at their forward edges where they are secured to the lips I22, and slightly spaced at their trailing edges to permit transverse blade flexing without deformation, or they may be spaced apart for the entire .width about one-sixty-fourth of an inch, as

shownvinli'ig. 7. 7

In Figs. 10 and 11, one means-for securing the strength member I02 to the mounting member 104 is shown. 'The mounting member I04 is provided with a generally square sectioned extension I50 which is inserted between the box spar formed by the webs I I0 into registry with bolt holes provided in the web and in the surface forming por tionsof the strength member I02. A spacer plug 152 formed to fit the inside of the box-like tube is inserted ahead of the extension I50 and into registry with other bolt holes. A pair of bolster plates I54 are. placed on the upperand lower surfaces of the member I02 through which pass bolts I56 through holes in the plates in the strength member I02 and in the extension I50 to secure all these parts together solidly; Transverse bolts I58 pass through webs I I0 and through the extension I50 to further, strengthen the structure adjacent the root. All of the holes and dimensions of the bolster plates I54 are such as to not weaken any of the structure of parts to which they are attached, but rather to strengthen the same. Fig S112 and 13, are plan and sectional viewsof the tip I08, also showing themethod of securing it to the outerend'of the blade I00. 7

The tip I 00 is built upon a-wooden spar I60 which slips into the tube part formed by the webs H0 and is secured by suitable rivets or bolts I62 which pass through holes in the tip of the strength memberfil02 and through holes I64 of the wooden spar. The tip I08 may be made en ,tirely of sheet metal formed intoa leading edge part-I66 'formedover a ,wooden shaping block I61: and a trailing part I68, which is riveted at thetrailing edge I10. The inboard end N2 of the trailing part I68 may abut the outboard trailing edge box of the blade I00 and the .for- .wardpart thereof is'iriveted as at M4 to the strength member I02. Ribs II6 are fastened to the spar- I60 and riveted to the trailing portion new provide strength to the tip portion I08.

. blade will have uniform characteristics for each unit "of its length.

Figs; 14 and 15show a second modification of the blade mounting; A'third'modification of the 6 form of the blade leading edge is shown in section (Fig. 15) at its inboard end, which section is typical for any section of the strength member.

Referring in detail first to Fig. 15, a blade spar and strength member 200 is of substantially the same exterior shape as the spars described above, but has in the leading edge a groove 202 for receiving a heater wire 204 for supplying heat to the leading edge of the blade for de-icing or preventing the formation of ice upon the same. The wire 204 may be of any suitable capacity for handling loads sufilcient for melting ice formation from the leading edge and far enough back from the leading edge to prevent a serious change .in the weight or'in theaerodynamic characteristics ofthe blade, in a manner well-known in the de-icing art. The spar 200 is adapted to support trailing edge forming boxes of the same kinds described above in connection with the other modifications.

The spar 200 is mounted in a step plate support comprising an inner plate 206 secured to a mounting member 208 having ears 2 I0 for securing the same to the rotor hub. The innerplate 206 'is placed against a phenolic plate 2I2 which in turn mates with the exterior of the spar 200' in part and with a spacer 2 I4 fitted to the shape of the leading edge of the blade. Spacer blocks 2 I 6 are inserted inside of the spar 200 so that when bolts 2 I8 are drawn up tight, the blade will not be deformed. By such construction of the sup- -port structure, high-centrifugal loads can be safely absorbed in the support so that this modification of the invention is better adapted for larger blades than the modification previously described. i

While I have shown and descri-bed'difierent modifications of the present improved rotor blade made up around a rugged strength member in which the weight balance portions thereof are formed so as to add strength to the blade, and

hollow longitudinal strength member having.

blade contour formingwalls, theupper and lower walls .being of a thickness to maintaingstresses therein below a predetermined maximumwalue during operation thereof, and'merging into a leading edge which is thicker to add strength and to position the transverse centerof gravity ofthe blade, said leading edgehaving a spanwise recess therein, at least one strengthening web between the upper and lower walls, and a, heater for de-icing saidblade disposed in said recess.

2. A variable pitch rotor blade for helicopters comprising a hollow longitudinal leadingxedge and spar member having upper and lower" blade contour forming walls merging into a common leading edge and having vertically spaced trailing edges, two spanwise extended webs connecting said upper and lower walls which are spaced chordwise'from said leading and trailing edges toforma socket of uniform cross section through outthelength of said spar memberwhich' is spaced from said leading and trailingedges by spanwise extending chambers, ablade root mem ber"'attached to said spar member, "a'blade" tip member havinga spar extension receivable in the outboard end'of said socket, and fastening members extending through said upperand lower walls and said extension.

.3. A variable pitch'rotor blade for a helicopter comprising a hollow longitudinal leading edge and spar member of uniform cross section throughout its length, said spar member having upper and lower blade contour forming walls of substantial thickness terminating in vertically spacedtrailing edges, two sp'anwise extended webs connecting the upper and lower walls of said member throughout the length of the latter and forming a box-like tube-through which thelongitudinal pitch changing axis of the blade extends, al blade root member having an outboard extension adapted to be fitted in the inboard end of 'said tube andconforming to the cross section of the latter, hollow closed boxes'arranged in spanwise spaced relation along said sparmember comprising V-shaped upper and low'erwalls having their spanwise aligned apexes forming the trailing edge of the blade and having their vertically spaced forward edges secured to said trailing edges of said spar member, and chordwise plates forming closures for adjacent ends of said blades, a blade tip member forming aclosure for the outboard, end of said blade having an inboard spar extension receivable in the outboard end of saidqtube, and fastenersextending through the upper and lower walls of said spar member and through said inboard and outboard extensions. 4. A rotor blade for helicopters including a longitudinal leading edge and spar member forming. a substantial chordwise portion of the blade and having upper and lower blade contour formingwalls terminating in vertically spaced trailing edges, a plurality of spanwise arranged trailing edge boxes forming the remainder of the chordwiseextent of the blade having upper and lower surface members, said surface members having their forward edges spaced vertically apart and secured to the trailing edges of said spar member and having their aft edges secured together and forming the trailing edge of the blade, the adjacent boxes having their chordwise edges spaced 'apart', and chordwise internal closure membersconnected to the upper and lower surface members of each box adjacent the chord- Wise edges thereof and forming closed sides for .contour forming walls comprising a'substantial chordwi'se portion of the blade and terminating in upper and lower trailing edges, a plurality of spanwisesheet metal trailing edge boxes form ing the remainder of the chordwise extent of the bladecomprising' upper and lower surface mem-,- bers having their forward edges secured to respectiveupper and lower trailing'edges of said extrusion and having their aft edges secured integrally together and forming the trailing edge of :the blade, and chordwise disposed sheet metal ribs forming closures for the sides of said boxes, said ribs'having upper and lower flanges which abut the upper and lower internal surfaces of saidboxes and are rigidly secured thereto.

.6. A- metal rotor blade for a helicopter including a longitudinal leading edge and spar extrusion, said extrusion having upper and lower blade contour forming walls comprising, a substantial chordwise portion of the blade and terminating upperfand lower trailing edges, a plurality of spanwise sheet metal trailing edge boxes forming the remainder of the chordwise extent of the blade comprising upper and lower surface members having their forward edges secured to respective upper and .lower trailing edges of said extrusionand havingtheir aft edges secured together and forming th trailing edge of the blade. cliordwise disposed sheet metal ribs forming closures for the sides of said boxes, said ribs having upper and lower flanges which abut the upper and lower internal surfaces of said boxes and are rigidly secured thereto, and spanwise closure members for the fronts of said boxes, 'each of said front closure members having flanges rigidly secured to said upper andlower surfaces of said boxes.

' 7 A metal rotor blade for helicopters comprisa ing' a hollow longitudinal leading'edge and spar member having upper and lower-walls which'forin a substantial chordwise portion of the blade and having a plurality of integralspanwis'e webs connected to said walls at points aft-'ofthe-leagdlng edge of said blade to form a load carrying'spa'r member of substantially uniform crossse'ction iroughout the length of the blade, reinforcing plate'means rigidly secured to the outer surface of said spar member at the root end thereof having reduced thickness in an outboard direction along said member, and a blade root'mounting fitting having plate means overlying and rigidly secured to the inboard portion of'said reinforcing plate means and to said member.

8. A metal rotor bladefor helicopters comprising a hollow longitudinal leading edge and spar member having upper and lower walls which form a substantial chordwise portion of the blade and having aplurality of integral spanwise lwebs connected to said walls at points aft of thelead; ing edge of said blade tov forina loadc arryi'ng Sparmember of substantially uniform crossselce tionthrougl'iout the lengthof the blade, reinforcing plate means rigidly secured to the outer surface of said spar member. at the root end thereof having -reduced thickness in an outboard dlrec tion along said spar, a blade root mounting fitting having plate means overlying .saidreinforcing plate means and secured to the latter and to said spar member, and a sheet of'non-metalliczm'a terial interposed between said fitting and "saidreinforcing plate means. I .I I 9-.'- A rotor 'blade for h elicopters 'i'nclu'ding'e longitudinal leading edge and sparmember forming a substantial chordwise 'portion'of the blade and having upper and lower blade contour forming walls terminating in vertically spaced trailing edge o uter surfaces, a plurality of sp'anwise ar ranged V-sh aped trailing] edge boxes) having upper and lower Wallls'forming the remainder'of the chordwise extent of the blade, each'of said V-shaped boxes having {its forward. vertically spaced inner surfaces secured tosaid outer trail ing edge surfaces of. said.,spar. and.havingflthe common trailing edge .of the upperand, lower wallsof theseveral boxes forming the trailing edge of the-blade, the adjacent boxes having their chordwise edges spaced apart, and; chor dwisegin ternal closure members connected to the upper and'lower walls of each box ad3'acent-the;chordwise edges thereof and-forming closed sides for saidboxes.-.-.

9 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Korf July 2, 1912 Page Sept. 23, 1919 Rohrbach Mar. 10, 1931 Whitworth Feb. 26, 1935 Howard Aug. 11, 1936 Stanley Feb. 15, 1938 Bennett Apr. 4, 1939 Bennett Dec. 12, 1939 Thomson Feb. 4, 1941 Number Number 

